To further dissect the folding mechanism of the Tetrahymena ribozyme, we are exploring, in collaboration with Dr. Williamson and his co-workers (currently at Scripps Institute), the folding of several fast-folding mutants of the Tetrahymena thermophila group I intron. These mutations are of particular interest in that they are all located within the P4-P6 domain although they profoundly influence the folding of the catalytic core of the ribozyme. Dr. Williamsons group has characterized the temperature and urea dependence of folding Hof these mutants, using their oligonucleotide-hybridization method, Hwhich probes the formation of helix P3 in the ribozyme. owever, this Happroach is unable to probe the fast transitions that can be followed Hby synchrotron footprinting. In order to measure the rates of folding Hof the rest of the 400 bases-long RNA, Martha Rook, a graduate student Hin Williamsons lab conducted a preliminary series time-resolved x-ray footprinting experiments on these mutants in collaboration with the Resource Center.